ln recent years, we and others have determined that at least one endothelial process, in addition to NO and cyclooxygenase metabolites, dilates cerebral vessels. This new process, termed "endothelium-derived hyperpolarizing factor" or EDHF, is likely an important dilator mechanism in the cerebral circulation during normal physiological states and following pathological conditions. In the proposed studies, we will address the mechanism of EDHF in cerebral arteries. The major hypothesis to be tested is that tandem-pore domain potassium channels are involved with the EDHF-mediated dilations in cerebral vessels of the rat. In order for the above hypothesis to be valid then all of the following specific aims must be true. (Specific Aim 1) Tandem-pore domain potassium channels must be present in cerebral arteries;(Specific Aim 2) activation of tandem-pore domain potassium channels must elicit dilation in cerebral arteries, and (Specific Aim 3) inhibition of tandem-pore domain potassium channels must inhibit EDHF-mediated dilations. In Specific Aim 1, we plan to use a combination of RT-PCR, Western analysis, immunohistochemistry, and electrophysiology to demonstrate the presence of the tandem pore domain potassium channels in cerebral arteries and, further, demonstrate that they are functional. In specific Aim 2, we will use isolated perfused cerebral arteries to determine if activation of these channels produces dilation. Furthermore, we plan to determine if inhibition of channel expression (anti-sense) and inhibition by pharmacological blockers antagonizes dilations produced by these potassium channels. In Specific Aim 3, we propose to determine if inhibition of tandem pore domain potassium channels inhibit EDHF-mediated dilations. Completion of the proposed studies will provide important insight into EDHF and its mechanism of circulatory control in brain. Furthermore, we anticipate that new information regarding tandem pore domain potassium channels will be a big step in the understanding of cerebral circulatory control.